Stretch control system for elongate material

ABSTRACT

System for controlling the speeds of rolls or the like in succeeding tandem stands of a rolling mill, or the speed of the rolls of a single stand operative with a take-up or pay-off reel, to produce a predetermined amount of stretch in elongate material passing through the mill. This is accomplished by generating alternating current signals whose frequencies are proportional to the speeds of succeeding stands in a tandem mill, for example, and by utilizing these signals to generate a direct current signal proportional to the difference in respective frequencies, and, hence, the difference in speeds. The value of this latter signal is then compared with a reference value to vary the speed of the second stand or a reel to maintain a substantially constant stretch relationship for the material.

United States Patent Hilsenbeck 1 1 Dec. 26, 1972 s41 STRETCH CONTROL SYSTEM FOR 3,556,510 1/1971 Treff ..226/25-X ELONGATE MATERIAL Primary Examiner-Allen N. Knowles [72] inventor. lliagrence L. Hilsenbeck, Lancaster, Assistant Examiner Gene A Church Attorney-F. H. Henson and R. G. Broadahl [73] Assignee: Westinghouse Electric Corporation, I

Pittsburgh, Pa. [57] ABSTRACT [22] Filed: March 3, 1971 System for controlling the speeds of rolls or the like'in succeeding tandem stands of a rolling mill, or the [211 App! 120586 speed of the rolls of a single stand operative with a take-up or pay-off reel, to produce a predetermined [52] US. Cl, ..318/7, 226/25, 226/ 195, amount of stretch in elongate material passing through 72/ the mill. This is accomplished by generating altemat- [51] Int. Cl. 865 h 59/38 ing current signals whose frequencies are proportional [58] Field of Search ..226/l95, 25; 318/7 to the speeds of succeeding stands in a tandem mill, for example, and by utilizing these signals to generate [56] Refere c C te a direct current signal proportional to the difference in respective frequencies, and, hence, the difference in UNITED STATES PATENTS speeds. The value of this latter signal is then compared 3,485,427 12/1969 Busker ..226/2s wi a reference value to vary the speed of the second 3,032,245 /1962 George et a1. ..226/25 UX stand or a reel to maintain a substantially constant 3,613,975 10/1971 Knight ..226/ stretch relationship for the material, 3,561,654 2/1971 Greinet ..226/25 3,087,663 -1r4/l963 Anderson ..226/44 9 Claims, 1 Drawing Figure l6- l6 lO- 47 |0 |2 -12 18- -18 26? Esln an;

11 m Esm (o t M2 FREQUENCY DIFFERENCE GENERATOR Esin Eposl zlt E cosi )1. l lL' l' l'i 7 12525552012 RESSEETDOR fag E Mlg-Gh I 1 SPEED REFERENCE ?1 L24 FREQUENCY 4 A k. co esgi n ""4'4 /5\ 36) 5,42

FREQUENCY T0 0.0 CONVERTER STRETCH CONTROL SYSTEM FOR ELONGATE MATERIAL BACKGROUND OF THE INVENTION There are certain applications, such asrolling mills for metal strip material, where it is necessary to maintain a certain degree of stretch or tension in the strip passing between a pair of cooperative stands in a tandem mill, or between a singlestand and acooperative take-up or pay-off reel. In the past, material stretch 1 Since in this system sampling is used, the accuracy is poor at lower speeds where the sampling times are longer.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided first and second spaced rotary means between which elongate material passes such that the stretch produced in the material between the rotary means will be dependent upon the relative angular speeds of the rotary means. In most cases, the rotary means will comprise work rolls in succeeding stands of a tandem rolling mill; however in certain cases one of the two rotary means may comprise a take-up or pay-off reel, provided that the system of the invention incorporates control means for compensating for variations in the diameter of the coil on the reel.

Coupled to each rotary means is a generator which produces electrical signals whose frequencies are proportional to the speeds of the respective rotary means. These signals are then utilized to generate at least one frequency componenthaving a frequency equal to the difference in frequencies of the two signals from the generators. In one embodiment of the invention shown herein, the two signals are modulated, one with the other, to produce a signal containing three frequency components, one of which has a frequency corresponding to the frequency of one of the two signals applied to the modulator, another of which has a frequency corresponding to the sum of the frequencies of the two modulated signals and the third of which has a frequency corresponding to the difference in frequencies of the two signals applied to the modulator. By applying the output of the modulator through a filter, all signals other than the difference frequency signal can be eliminated. This difference frequency signal is then applied to a frequency-to-direct current converter whereby the output of the converter will be a direct current signal proportional to the difference in frequency of the two signals and, hence, the difference in speeds of the two rotary means. This difference signal is then compared with a reference signal, proportional to the desired difference in speed; and if the two are not the same an error signal is produced for varying the speed of the second rotary means until the desired stretch is achieved. It should be understood that while modulation is shown herein'as the principal means of obtaining a difference frequency signal, other teclllmiques, such as multiplication, can be used equally we Since the magnitude of the reference signal, proportional to the desired difference in speeds of the two rotary means, will be dependent upon the speed of the elongate material passing through the mill, control 0 means must be provided for varying the reference signal as the speed of the material changes. This is preferably accomplished by the use of a'frequency-todirect current converter coupled to the generator for one of the two rotary means, and by applying the output of this frequency-to-direct current converter to a rheostat from which the reference signal is derived.

In the case where one of the two rotary means comprises a take-up or pay-off reel for a rolling mill, additional means must be included to compensate for the increase or decrease in the coil diameter of material on a given reel which, of course, will vary the speed of that particular reel without regard to the stretch or tension produced in the strip.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying single FIGURE drawing which schematically illustrates one embodiment of the invention.

With reference now to the drawing, an illustrative embodiment of the invention is shown and includes a pair of stands S1 and S2 of a multi-stand rolling mill. Each stand S1, S2 includes a pair of work rolls l0 and 12 through which strip material 14 under tension passes. The work rolls 10 and 12 in each stand are backed up by backup rolls l6 and 18. The rolls of stand S] are driven by means of a drive motor M1 connected to a generator G1, the motor-generator set being controlled by a speed regulator 20. Similarly, the rolls of stand 82 are driven by motor M2 connected to generator G2, the motor-generator combination being controlled by speed regulator 22. Both speed regulators 20 and 22 receive a speed reference signal on lead 24.

By driving the rolls of stand S2 at a speed higher than those of stand S1, tension or stretch will be produced in the strip material 14 between the two stands. Furthermore, the amount of tension or stretch will be a function of the difference in speed of the two stands.

Connected to the backup roll 18 of stand S1 is a generator 25 which produces a signal on lead 26 proportional to:

E sin w,t

where w, is a function of the angular velocity of the rolls of stand S1. Similarly, the backup roll 18 of stand S2 is connected to a second alternating current generator 28 which produces on lead 30 an alternating current signal which can be represented as:

E sin w t where (0 is a function of the angular velocity of the rolls of stand S2. The two signals on leads 26 and 30 are applied to frequency difference generator 32 where the signal E sin m t is modulated with the signal E sin cu t. That is, E sin w t corresponds to the modulating signal while E sin (0 corresponds to the carrier frequency.

In accordance with well-known modulation techniques, modulation of this type will produce three fixed-amplitude harmonic voltages, the first having the frequency of the carrier, the second having a frequency equal to the carrier frequency minus the signal frequency, and the third having a frequency equal to the sum of the carrier and signal frequencies. The second and third components are termed sideband frequencies. Thus, at the output of the modulator three signals will appear, namely, E sin w t, E cos (w, m and E cos (w (0,) t, where E and E represent different voltage magnitudes.

By passing the three signal frequencies through a low-pass filter 34, only the lowest frequency component, namely, E cos (m w )t will remain. This v signal, in effect, will vary in direct proportion to the difference in speeds of the two stands S1 and S2. It is applied to a frequency-to-direct current converter 36 which will produce at its output a direct currentsignal proportional to the difference in speed.

At the same time, the signal E sin 0,! on lead 26 is applied to a second frequency-to-direct current converter 38 such that the output of the circuit 38 will be a direct current signal proportional to the speed of stand S1. This is applied to a potentiometer 40, the movable tap of which is connected through resistor 42 to summing point 44. At the same time, the output of the frequency-to-direct current converter 36 is also applied through resistor 46 to the summing point 44. The summing point 44, in turn is connected to the input of an integrating summing amplifier 48 having a feedback path including a capacitor 50. The output of the summing amplifier 48 is applied to the speed regulator 22 for stand S2 as well as the signal at the output of the frequency-to-direct current converter 38.

In the operation of the system, the signal on the tap of potentiometer 40 provides a reference signal which is compared with the signal at the output of circuit 36 proportional to a difference in speed. Since the amount of stretch will vary depending upon the speed of the strip, it is necessary to vary the reference signal as the strip speed varies, and this is provided by way of the frequency-to-direct current converter 38. The output of the integrating amplifier 48 is used as a vernier motor speed reference to the speed regulator 22. Since the output of the frequency-to-direct current converter 36 is unidirectional, it is not indicative of which drive is traveling at a faster speed. It is for this reason that the output of the frequency-to-direct current converter 38 is applied to'the speed regulator 22 to insure that the I rolls in stand S2 are always rotating at a speed greater than those in stand SI.

Should the tension of the strip as represented by the output of circuit 36 fall, then the comparison of this signal with that established by the tap on potentiometer 40 will produce a signal of one polarity at the input to amplifier 48, causing the speed regulator 22 to increase the speed of the rolls of-stand S2 until the error signal is reduced. On the other hand, if the tension should rise above the present value as determined by the position of the top on rheostat 40, then an error signal of the opposite polarity will be produced at the summing point 44, causing the speed regulator 22 to decrease the speed of the rolls of stand S2 until the tension is reduced to the point where the error signal is again zero.

As was mentioned above, the system is also applicable to single-stand rolling mills, for example, wherein tension is regulated by means of take-up and pay-off reels. In this case, the speed regulator 22 would be connected to the drive motor for the take-up or pay-off reel; however additional means would have to be incorporated to compensate for variations in the angular velocity of the take-up or pay-off reel as a result of increases and decreases in the diameter of the coil on the reel.

The difference frequency generator 32, instead of comprising a modulator, may take different forms of suitable computer apparatus to electrically perform any one of the following mathematical computations:

2 sin W x sin w t= 1/2 [cos (m -10 M cos w,+ 2) 1 (4) cos (a t X cos w t l/2 [sin (w +tu )t sin (w,-

zfi

(5) sin w t cos wit cos w,z sin (0 sin ((0 -8 (6) cos (0,! sin 00 1+ sin w,t cos w t= cos (co -m In the case of Equations l-4 above, an electrical multiplier is required as well as a filter similar to filter 34 for separating the plus and minus frequency components. Also, in the case of Equations 1, 3 and 4, and assuming that the signals from generators 25 and 28 are sine functions, phase shift networks would have to be introduced to produce the cosine functions.

In the case of Equations 5 and 6, signal multipliers and an adder or subtractor would have to be used, but no filter similar to filter 34 is needed, After the difference signal is derived, regardless of the means used, the operation of the circuit isthe same as that described above.

Although the invention has been shown in connection with a certain specific embodiment, it will .be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention. In this respect, it is apparent that the speed of the first set of rolls, rather than the second set, can be varied to produce the same overall result. That is, when the tension decreases, the speed of the first set of rolls would be decreased and vice versa, assuming that the speed of the second set of rolls is maintained essentially constant.

I claim as my invention:

1. In combination, first and second spaced rotary means between which elongate material passes'such that the stretch produced in the material between said first and second rotary means will be dependent upon the respective angular speeds of the rotary means, means for producing a first electrical signal proportional to the angular velocity of said first rotary means, means for producing a second electrical signal proportional to the angular velocity of said second rotary means, means responsive to said first and second signals for producing a third electrical signal which varies as a function of the difference in angular velocities of the first and second rotary means and therefore varies as a function of the stretch in the material between the rotary means, means for producing a fourth electrical signal which is proportional to the desired stretch produced in the material between the first and second rotary means, means for comparing said third and fourth electrical signals to produce an error signal, and means responsive to said error signal for varying the speed of at least one of said rotary means until said third and fourth electrical signals are substantially equal and said error signal is substantially equal to zero.

2. The combination of claim 1 wherein the speed of the second one of said rotary means in the pathof travel of said elongate material is varied.

3. The combination of claim 1 wherein said spaced rotary means comprise spaced rolls through which said elongate material passes.

4. The combination of claim 3 wherein said elongate material comprises metal strip material and said spaced rolls comprise the work rolls of succeeding stands of a tandem rolling mill.

5. The combination of claim 1 wherein said means for producing a third electrical signal includes a modulator.

6. The combination of claim 1 wherein said first and second signals are alternating current signals and including first and second alternating current generators for producing the respective first and second alternat-- ing current signals, means for modulating said first alternating current signal with said second alternating current signal, and a filter connected to the output of second frequency component equal in frequency to the difference in frequencies of said first and second alternating current signals, and a third frequency component equal in frequency to the sum of the frequencies of said-first and second alternating current signals, said filter passing said second frequency component while rejecting said first and third frequency components.

8. The combination of claim 7 including means for varying the magnitude of said third electrical signal as a function of the angular velocity of one of said rotary means.

9. The combination of claim 8 wherein said third electrical signal is varied as a function of the angular velocity of the first of said rotary means in the path of travel of said elongate material. 

1. In combination, first and second spaced rotary means between which elongate material passes such that the stretch produced in the material between said first and second rotary means will be dependent upon the respective angular speeds of the rotary means, means for producing a first electrical signal proportional to the angular velocity of said first rotary means, means for producing a second electrical signal proportional to the angular velocity of said second rotary means, means responsive to said first and second signals for producing a third electrical signal which varies as a function of the difference in angular velocities of the first and second rotary means and therefore varies as a function of the stretch in the material between the rotary means, means for producing a fourth electrical signal which is proportional to the desired stretch produced in the material between the first and second rotary means, means for comparing said third and fourth electrical signals to produce an error signal, and means responsive to said error signal for varying the speed of at least one of said rotary means until said third and fourth electrical signals are substantially equal and said error signal is substantially equal to zero.
 2. The combination of claim 1 wherein the speed of the second one of said rotary means in the path oF travel of said elongate material is varied.
 3. The combination of claim 1 wherein said spaced rotary means comprise spaced rolls through which said elongate material passes.
 4. The combination of claim 3 wherein said elongate material comprises metal strip material and said spaced rolls comprise the work rolls of succeeding stands of a tandem rolling mill.
 5. The combination of claim 1 wherein said means for producing a third electrical signal includes a modulator.
 6. The combination of claim 1 wherein said first and second signals are alternating current signals and including first and second alternating current generators for producing the respective first and second alternating current signals, means for modulating said first alternating current signal with said second alternating current signal, and a filter connected to the output of said modulating means, with said third electrical signal appearing at the output of said filter.
 7. The combination of claim 6 wherein said modulating means produces a first frequency component equal in frequency to one of said alternating current signals, a second frequency component equal in frequency to the difference in frequencies of said first and second alternating current signals, and a third frequency component equal in frequency to the sum of the frequencies of said first and second alternating current signals, said filter passing said second frequency component while rejecting said first and third frequency components.
 8. The combination of claim 7 including means for varying the magnitude of said third electrical signal as a function of the angular velocity of one of said rotary means.
 9. The combination of claim 8 wherein said third electrical signal is varied as a function of the angular velocity of the first of said rotary means in the path of travel of said elongate material. 